I just redid my closed chamber and the ceiling is 22 inches from the substrate. I have a mega-ray basking mercury vapor bulb 100 watt. I have the fixture as high up as it can go and the flat slate stone under the bulb reads 115 F with my heat gun! I have not put the tortoises in yet. I did a search and others say 95-100 is best. Do you think a different fixture would change anything? I'm using a silver ceramic socket fixture that you would get at a farm store for baby chicks. Since I can't raise the lamp and they do not make a bulb smaller than 100 watts. Any help would be appreciated. The 115 F is only directly in the center the rest of the stone is 105F. I am using four 34" arcadia D3+ High output bulbs in the t5 HO fixtures. Should I just skip the mercury vapor bulb and get a 65 watt flood bulb for basking? my enclosure is 4'x8'. Thanks in advance.